Single element three terminal piezoresistive pressure sensor

Abstract

Embodiments of the invention provide for three-terminal pressure sensors (“3-TPS”), a method of measuring a pressure with a 3-TPS, and a method of manufacturing a 3-TPS. In some embodiments, the 3-TPS includes a semiconducting layer with cavity and a 3-TPS element having at least one piezoresistive layer overlapping at least a portion of the cavity and oriented at an angle selected to provide a desired sensitivity for the 3-TPS. The method of measuring a pressure with a 3-TPS is performed with a 3-TPS that includes an input terminal, first and second output terminals, and a 3-TPS element, the 3-TPS element overlapping at least a portion of a cavity at a predetermined angle. The method comprises providing an input signal to the input terminal of the 3-TPS, determining a difference between two output signals from the respective output terminals of the 3-TPS, and correlating the determined difference to a pressure.

What is claimed is: 
     
       1. A three terminal pressure sensor (“3-TPS”), comprising: a first semiconducting layer having a substantially circular cavity; an insulating layer configured on the semiconducting layer, at least a portion of the insulating layer overlapping the cavity; a second semiconducting layer configured on the insulating layer; and a 3-TPS element, at least a portion of which is configured on the second semiconducting layer, the 3-TPS element comprising: at least one piezoresistive layer having a length of at least about 40 μm and a width of at least about 20 μm; an input terminal; and first and second output terminals, wherein the 3-TPS element includes at most three terminals and overlaps at least a portion of the perimeter of the cavity, wherein the 3-TPS element is oriented at an angle of about 45 degrees from a tangent line to the perimeter of the cavity, and wherein at least a portion of the first or second output terminals overlaps the cavity and at least a portion of the input terminal does not overlap the cavity. 
     
     
       2. A method of manufacturing a three terminal pressure sensor (“3-TPS”), comprising: fabricating a 3-TPS element that overlaps at least a portion of a cavity, the 3-TPS element having an angle at which the 3-TPS element is configured across the at least a portion of the cavity; and fabricating an input terminal and first and second output terminals in communication with the 3-TPS element.; wherein the 3-TPS element includes at most three terminals. 
     
     
       3. The method of  claim 2 , wherein the 3-TPS element has a length of at least about 40 μm. 
     
     
       4. The method of  claim 2 , wherein the 3-TPS element has a width of at least about 20 μm. 
     
     
       5. The method of  claim 2 , wherein the angle is about 45 degrees from a tangent line to the perimeter of the cavity. 
     
     
       6. The method of  claim 2 , wherein the angle is about 45 degrees from a <110> direction of a silicon-on-insulator wafer upon which the 3-TPS element is fabricated. 
     
     
       7. The method of  claim 2 , further comprising:
 fabricating a diaphragm layer between the 3-TPS element and a second layer that includes the cavity. 
 
     
     
       8. The method of  claim 2  wherein the first and second output terminals are separated by a gap of about 3 μm. 
     
     
       9. The method of  claim 2 , wherein the cavity is substantially circular. 
     
     
       10. A three terminal pressure sensor (“3-TPS”), comprising: a semiconducting layer having a cavity; and a 3-TPS element having at most three terminals and at least one piezoresistive layer overlapping at least a portion of the cavity and oriented at an angle selected to provide a desired sensitivity for the 3-TPS. 
     
     
       11. The three terminal pressure sensor of  claim 10 , further comprising:
 an insulating layer configured between the semiconducting layer and the 3-TPS element. 
 
     
     
       12. The three terminal pressure sensor of  claim 10 , further comprising:
 a second semiconducting layer upon which the 3-TPS element is configured. 
 
     
     
       13. The three terminal pressure sensor of  claim 10 , wherein the at least one piezoresistive layer includes at least one p-type boron implant region. 
     
     
       14. The three terminal pressure sensor of  claim 10 , wherein the at least one piezoresistive layer is oriented at an about 45 degree angle relative to a <110> direction of a (100) n-type SOI wafer upon which the 3-TPS element is fabricated. 
     
     
       15. The three terminal pressure sensor of  claim 10 , wherein the at least one piezoresistive layer is oriented at an about 45 degree angle from a tangent line to a perimeter of the cavity. 
     
     
       16. The three terminal pressure sensor of  claim 10 , wherein the 3-TPS element has a length of at least about 40 μm. 
     
     
       17. The three terminal pressure sensor of  claim 10 , wherein the 3-TPS element has a width of at least about 20 μm. 
     
     
       18. The three terminal pressure sensor of  claim 10 , wherein the cavity is a substantially circular cavity. 
     
     
       19. The three terminal pressure sensor of  claim 10 , further comprising at least one contact disposed proximate the at least one piezoresistive layer and separated therefrom by a second insulator layer, the contact configured to apply a selected voltage across the at least one piezoresistive layer to control the sensitivity of the 3-TPS. 
     
     
       20. The three terminal pressure sensor of  claim 19 , further comprising a dual drain field effect transistor comprised of the at least one piezoresistive layer, the contact, the second insulator layer and the first, second, and third electrical terminals. 
     
     
       21. The three terminal pressure sensor of  claim 10 , wherein a first portion of the at least one piezoresistive layer communicates with an input terminal, wherein a second portion of the at least one piezoresistive layer communicates with a first output terminal, and wherein a third portion of the at least one piezoresistive layer communicates with a second output terminal. 
     
     
       22. A method, comprising: fabricating a three terminal pressure sensors (“3-TPS”) of the type that includes a 3-TPS element having at most three terminals and at least one piezoresistive layer overlapping at least a portion of a cavity and oriented at an angle selected to provide a desired sensitivity for the 3-TPS, wherein fabricating the  3 -TPS element includes at least one deep reactive ion etching step; and fabricating etched dicing streets along at least the perimeter of the 3-TPS during the at least one deep reactive ion etching step. 
     
     
       23. The method of  claim 22 , wherein the etched dicing streets eliminate a subsequent need for dicing the 3-TPS from a wafer and wherein the fabrication of the etched dicing streets is performed concurrently with the formation of the cavity.